This invention is generally directed to a mechanism for mechanically locking an air suspension system in a van-type trailer. More particularly, the invention contemplates a mechanism for locking the air suspension system to prevent up-and-down movement between the vehicle frame and the wheels of the van when a van is being loaded or unloaded at a loading dock.
This invention is intended to solve problems which arise when loading a van-type trailer having an air suspension. In general, such a suspension includes a wheel axle supported at the end of a cantilevered lever or arm having its opposite end rotatable about a fixed pivot. An air bag is located between the van frame and the axle for permitting the desired spring action. A tank of compressed air is provided on the van frame and a valve is connected between the tank and the air bag so as to adjust the pressure in the air bag for supporting the weight of the van and its load and more specifically, for substantially maintaining a predetermined spacing between the van frame and the axle, at least when the van is stationary or not subjected to road shocks.
When a van is to be loaded or unloaded, the trailer is backed against a loading dock which is generally level with the floor of the van. A board or "bridge" is put down between the loading dock and the floor of the van so that a fork-lift truck may be driven into and out of the van. When the front wheels of the fork-lift truck first move from the loading dock onto the back end of the van floor, a heavy load is suddenly placed on the air suspension which, for example, might be on the order of 30,000 pounds, and as a result the back end of the van will move downward suddenly as the air bags flatten. This causes the pivoted axle supporting arm to rotate about the pivot point in a clockwise direction. Since it is the general practice, if not the law, that the wheel be locked by a brake when the vehicle is parked for loading and unloading, the tire will also rotate around the pivot point in a clockwise direction which tends to force the trailer forwardly away from the loading dock as much as several inches. As a result, the board or "bridge" may fall out from between the dock and the van and the rear wheels of the fork-lift truck may fall into the gap between the loading dock and the van.
When the van is backed against the dock, the dock is routinely provided with a latch member that reaches out and engages beneath the back bumper of the trailer. If the trailer moves forward as mentioned above, the latch member engaging the bumper may cause the bumper to be pulled backwardly and bent. Furthermore, when the trailer body moves downwardly, the bumper may be forced downwardly onto the latch member which tries to support the weight of the van whereby the bumper may be bent and/or the latch member may be bent or broken.
If the fork-lift truck successfully enters the van, movement of the fork-lift truck toward the front end of the van for either loading or unloading, will shift the weight forwardly of the air suspension so that the air pressure in the bags which has been increased after the initial downward deflection sufficiently to again raise the bed of the trailer to the desired level, functions suddenly to raise the back end of the trailer further. This causes the suspension lever arm to pivot in a counter-clockwise direction along with a corresponding counter-clockwise movement of the tire. Since the tire is essentially unloaded, however, it tends to slip over the ground rather than to drive the trailer. In other words, the trailer will remain in the advanced position to which it has been pushed. As will be appreciated, repeated trips of the fork-lift truck into and out of the van will cause the trailer to "ratchet" forward. It will also cause repeated charging of the air bags and venting of the air bags until the compressed air in the accumulator is exhausted.
The present invention solves all of the above problems by providing a mechanism for mechanically locking the air suspension in the desired position when the van is first moved against the loading dock and parked. In general, a stiff leg or strut of fixed length is connected between the wheel axle and the van frame so as to prevent the air bag from either expanding or collapsing.